1. Field of the Invention
The present invention relates to a thin-film magnetic head manufacturing method and apparatus for precisely lapping thin-film magnetic heads for use in magnetic disk devices and the like.
2. Description of the Related Art
In manufacturing thin-film magnetic heads, in general, thin layers constituting thin-film magnetic elements, such as insulating layers, magnetic layers, and conductive layers, are stacked in order on a substrate made of Al.sub.2 O.sub.3 --TiC (alumina titanium carbide) by sputtering, and the thin layers are worked by photolithography or ion milling as required.
In order to manufacture thin-film magnetic heads, plural thin-film magnetic elements 1 are formed in plural rows on a substrate 2, as shown in FIG. 5 (FIG. 5 shows only some of the thin-film magnetic elements 1). A thin-film magnetic element 1 is a so-called "MR (magnetoresistive)/inductive combined magnetic head" in which an MR magnetic head having a magnetoresistive sensor for reading recorded information and an inductive magnetic head for writing are combined. The thin-film magnetic elements 1 are electrically connected by electrodes 4 connected thereto. The substrate 2 is cut along the dotted lines to yield a slider bar as shown in FIG. 6.
In manufacturing a thin-film magnetic head, the height of the magnetoresistive sensor of the MR magnetic head in the thin-film magnetic element 1 must be adjusted to a predetermined value. The MR height is adjusted by lapping an ABS (air-bearing surface) 3a shown in FIG. 6 while using some of a plurality of magnetoresistive sensors as monitor elements, and measuring DC resistance values (DCR values) between the electrode layers connected to both ends of the magnetoresistive sensors.
By lapping the ABS 3a until the DCR value fall into the finish tolerances, the height of the magnetoresistive sensors (MR height) can be set at an appropriate value. After the MR height is adjusted, the slider bar 3 is cut along the dotted lines shown in FIG. 6 into individual thin-film magnetic heads. Individual substrates cut from the slider bar 3 serve as sliders. The ABS 3a of the slider faces a recording medium and receives a levitating force when the recording medium moves.
Lapping for adjusting the MR height is performed by using, for example, a lapping plate 21 shown in FIG. 8. The slider bar 3 shown in FIG. 6 is placed so that the ABS 3a thereof is in contact with the surface of the lapping plate 21. The lapping plate 21 is rotationally driven to lap the ABS 3a of the slider bar 3.
FIGS. 9A and 9B are flowcharts showing the process of lapping for adjusting the MR height.
Lapping is performed in two stages, rough lapping (FIG. 9A) with a lapping fluid applied on the upper surface of the lapping plate 21, and finish lapping (FIG. 9B) with a lubricant applied on the lapping plate 21 as necessary.
In rough lapping, as shown in FIG. 9A, lapping is continued while the DCR values of the monitor elements are being monitored, and is completed when the DCR values fall into a predetermined DCR range.
In finish lapping shown in FIG. 9B, lapping is similarly performed while the DCR values of the monitor elements are being monitored, and it is completed when the DCR values fall into the finish tolerance range, which means that the MR heights also falls into the finish tolerance range.
In a conventional lapping method, as shown in FIGS. 9A and 9B, however, a level difference is likely to remain between the ABS 3a of the slider bar 3 and the thin-film magnetic element 1 in a completed thin-film magnetic head.
FIGS. 11A and 11B are side views of the slider bar 3 and the thin-film magnetic element 1, respectively, before lapping is started, and during or after lapping. When the thin-film magnetic element 1 is formed (the process shown in FIG. 5), a cover layer 5 is formed to cover the thin-film magnetic element 1. This cover layer 5 is made of Al.sub.2 O.sub.3 or SiO.sub.2.
In rough lapping, as described with reference to FIG. 9A, the lapping fluid contains fine particles, and the ABS 3a is lapped therewith.
The thin-film magnetic element 1 primarily made of Al.sub.2 O.sub.3, NiFe (permalloy), or the like is lapped at a higher rate than the slider bar 3 made of Al.sub.2 O.sub.3 --TiC (alumina titanium carbide) or the like. Therefore, as shown in FIG. 11B, a level difference is likely to be formed between the ABS 3a of the slider bar 3 and a surface la of the thin-film magnetic element 1 opposing the recording medium in rough lapping.
In particular, in rough lapping with the lapping fluid applied on the surface of the lapping plate 21, the opposing surface la of the thin-film magnetic element 1 is likely to be lapped at a high rate by the fine particles in the lapping fluid, which increases the amount of level difference (recession). Hereinafter, the amount of level difference (recession) is represented by the letter "R". The recession R is zero when the opposing surface 1a of the thin-film magnetic element 1 is flush with the ABS 3a of the slider bar 3, and the direction in which the recession R increases is designated the film "positive (+) direction".
Since rough lapping, as shown in FIG. 9A, is performed while monitoring only the DCR values of the magnetoresistive sensors, when the DCR values fall into a predetermined range, that is, when the heights of the magnetoresistive sensors (MR height) fall into a predetermined range, it is impossible to determine the extent to which the ABS 3a of the slider bar 3 has been lapped. For this reason, even when the opposing surface la of the thin-film magnetic element 1 has been sufficiently lapped and the MR height values are within the predetermined range, the ABS 3a of the slider bar 3 has not been sufficiently lapped and a substantial recession R is produced in the positive direction.
In the subsequent finish lapping process, the opposing surface 1a of the thin-film magnetic element 1 is lapped at a higher rate than the ABS 3a of the slider bar 3. Therefore, in a case in which a substantial recession R is produced during rough lapping, that is, when a great difference remains in the levels between the ABS 3a of the slider bar 3 and the opposing surface 1a of the thin-film magnetic element 1, if finish lapping is performed while monitoring only the DCR values, as shown in FIG. 9B, a substantial recession R remains when the DCR values of the thin-film magnetic element 1 falls into the finish height tolerances.
That is, although too large a recession R remains at the completion of rough lapping, and the ABS 3a of the slider bar 3 is not lapped to sufficiently reduce the recession R due to a short finish lapping time, finish lapping is completed.
Because of the need to cope with recent increases in density of recording media, thin-film magnetic heads have been required to minimize the distance between the opposing surface of the thin-film magnetic element and a recording medium in a driving state to reduce spacing loss as much as possible. If a substantial recession is produced in such a thin-film magnetic head as described above, the spacing loss increases, and this impairs writing/reading characteristics.
In general, the lapping plate 21 is rotated at approximately 100 rpm for the purpose of lapping. Conventionally, the lapping plate 21 is controlled by trapezoidal driving so that the power applied to a motor for driving the lapping plate 21 is switched from the driving state to a stop state at the completion of finish lapping. When the lapping plate 21 rotating at a high speed is rapidly stopped at the completion of finish lapping, flaws are produced on the ABS 3a of the slider bar 3 and the opposing surface 1a of the thin-film magnetic element 1.
The flaws on the ABS 3a of the slider bar 3 remain unchanged on an ABS of the slider, floating characteristics on the recording medium becomes unstable, or flaws may be produced on the surface of the recording medium.